1. Field of the Invention
The present invention relates to a thermally assisted magnetic recording medium that is used in, for example, a hard disk drive (HDD) and a magnetic recording and reproducing apparatus.
2. Description of Related Art
In recent years, there has been an increasing demand for hard disk drives (HDD) with high capacity. As means for meeting the demand, a thermally assisted recording method has been proposed in which a magnetic head provided with a laser light source heats a magnetic recording medium to perform recording. The thermally assisted recording method heats the magnetic recording medium to significantly reduce coercive force. Therefore, a magnetic layer of the magnetic recording medium can be made of a material with a large crystal magnetic anisotropic constant Ku. As a result, it is possible to reduce a magnetic grain size while maintaining thermal stability and to achieve a surface density of about 1 Tbit/inch2.
An ordered alloy, such as an L10 FePt alloy, an L10 CoPt alloy, or an L11 CoPt alloy has been known as the magnetic material with a large crystal magnetic anisotropic constant Ku. In addition, an oxide, such as SiO2 or TiO2, C, or BN is added as a grain boundary layer material to the magnetic layer in order to divide crystal grains made of the ordered alloy. When the magnetic layer of the magnetic recording medium has a granular structure in which magnetic crystal grains are separated in a grain boundary phase, it is possible to reduce the exchange coupling between the magnetic grains and to achieve a high signal-to-noise ratio (SNR).
An L1o ordered alloy in the magnetic layer needs to have a high (001) orientation in order to obtain a thermally assisted recording medium with high perpendicular magnetic anisotropy. The orientation of the magnetic layer can be controlled by an underlayer. Therefore, it is necessary to provide an appropriate underlayer in order to control the orientation of the magnetic layer.
For example, Patent Document 1 discloses a technique in which a MgO underlayer is used to make an L10 FePt magnetic layer have a high (001) orientation. In addition, Patent Document 2 discloses a technique in which a MgO underlayer is formed on an underlayer made of an alloy with a BCC structure, such as a CrTiB alloy, to make an L10 FePt magnetic layer have a high (001) orientation. Furthermore, Patent Document 3 and Patent Document 4 disclose a technique in which an L10 FePt magnetic layer is formed on an underlayer made of an alloy with a NaCl structure, such as TiN or CrN, to have a high (001) orientation.